1. Field of the Invention
This invention relates to a friction element for use in a friction clutch. Friction elements of the kind to which the invention relates are used connected to a clutch hub member to form the driven element of a type of friction clutch widely used, for example, in the drive line of heavy duty motor vehicles.
2. Description of Prior Art
A typical clutch driven element has a plurality of friction elements disposed about the circumference of a clutch hub member, each friction element having a friction facing engagable with a driving element of the clutch. The friction facing may be of sintered metallic and/or ceramic material, and many shapes have been proposed for such friction facings. Viewed in the direction parallel to the rotational axis of the clutch hub member, the shape of most friction facings has been a portion of an annulus of the material.
An example of a proposed more complex shape for a friction facing is disclosed in GB No. 2 137 706, equivalent to U.S. Pat. No. 4,565,274 the friction facing having arcuate generally radially extending, circumferentially leading and trailing, faces. Apart from such arcuate edges, however, the configuration of the friction facing is generally part-annular as above referred to.
It has been found, however, that a friction facing of such a shape is unnecessarily wasteful of material, and does not have desirable operating characteristics in terms of maintaining a satisfactory performance across the whole radial extent of the friction facing. It is to be understood that when we use the terms radially and circumferentially herein, we use them in relation to the rotational axis of the clutch disc.
It will be appreciated that in use the speed at which rubbing occurs at the surface of a friction facing is greater at a greater distance from the axis of rotation of the clutch disc, so that there is a greater generation of heat and tendency for the friction material to wear at such greater distance. To control temperatures across the friction facing by effectively providing a greater heat sink capacity, and to give more even wear, the amount of friction material at portions thereof where the rubbing speed is greater must be greater than that where the speed is less.